Loadboards are often used to calibrate and perform diagnostic tests on instruments used in automated test equipment (ATE). For example, a single loadboard coupled to an instrument may couple pins of the instrument for pin-to-pin calibration and diagnostics, whereas multiple loadboards may be coupled to couple pins of multiple instruments for instrument-to-instrument calibration and diagnostics. Given that modern integrated circuits utilize high speed signaling upwards of many gigahertz, loadboard coupled to instruments testing such high-speed devices under test (DUTs) must be able to conduct the high-speed signals with minimal signal degradation such that accurate and precise calibration and/or diagnostics may be performed.
FIG. 1 shows conventional ATE loadboard 100 for coupling to an instrument. As shown in FIG. 1, loadboard 100 includes a number of relays 110-150 for coupling pins 1 through 16 to the reference pin. The 16 pins couple to a 16 functional pins of an instrument, where each functional pin may be calibrated with respect to one another by adjusting the state of relays 110-150. For example, the state of the relays shown in FIG. 1 enables pin-to-pin calibration of pin 1 with respect to the reference pin by transmitting signals to and from the coupled pins as represented by communication path 160. The states of the relays may then be successively adjusted to couple the other 15 pins to the reference pin for calibration thereto. As such, all the pins may be calibrated to one another by calibrating each pin to the reference pin.
In addition to pin-to-pin calibration, the state of relay 150 may be adjusted to couple the reference pin of one instrument to that of another instrument using a loadboard similar to loadboard 100 for each coupled instrument. By first calibrating respective functional pins to the reference pin of an instrument, functional pins of coupled instruments may be calibrated with respect to one another by calibrating the reference pins of the coupled instruments with respect to one another.
Although loadboards similar to conventional loadboard 100 have been used in the past, the increased signaling speeds used by modern DUTs are beginning to exceed the capabilities of the relays. For example, signal degradation is common when using the relays to gate high-speed signals. Additionally, as the average number of devices tested by ATE increases, the space and power consumption of the relays present fiscal and other logistics issues for ATE manufacturers and users alike. Moreover, as the number of pins of an average DUT increases, the limited loadboard real estate is quickly used up, resulting in component placement which compromises signal integrity and other loadboard functionality.
Furthermore, conventional loadboard 100 requires that each functional pin be calibrated with respect to the reference pin given the inability to directly couple any two functional pins. As such, the need to switch relay state prevents parallel calibration, thereby increasing calibration time and cost. Additionally, calibration measurements of functional pins with respect to the reference pin must be compared to derive calibration data of functional pins with respect to other functional pins. In addition to adding an extra step, such comparison is likely to interject error due to hysteresis, tolerance buildup, or the like.
Thus, not only do relays affect the accuracy and precision of calibration measurements given the inherent signal degradation associated with the relays, but the need to compare measurements with respect to a functional pin exacerbates the problem by interjecting additional error. Furthermore, the decreased accuracy and precision also bring with them increased operation cost, ATE size and signal degradation given the switched nature, large size and power consumption of the relays.